Lens is a common optical element in an optical device. With the development of optical technology, the requirements for lenses are increasing. Fresnel lens, as a lens with small volume, light weight and easy for reproduction, is widely used in various optical devices.
Fresnel lens in the existing optical device may only converge light, and in some scenarios, for example, when the Fresnel lens is employed to generate heat by converging sun light so as to obtain solar energy, it is needed to adjust temperature. If the Fresnel lens converges light all the time, it is continuously performed for heating only and it is hard to adjust temperature. Therefore, there are limitations for application of the existing Fresnel lens.